1. Field of the Invention
This invention relates to a photoconductive composition, articles prepared from this composition and methods of use of said articles. More specifically, this invention involves organo-chalcogen compositions, electrophotographic imaging members wherein the photoconductive insulating layer comprises an organo-chalcogen composition, and an electrophotographic imaging process employing said imaging member.
2. Description of the Prior Art
The formation and development of images on the imaging surfaces of photoconductive materials by electrostatic means is well known. The best known of the commercial processes, more commonly known as xerography, involves forming a latent electrostatic image on the imaging layer of an imaging member by first uniformly electrostatically charging the surface of said layer and then exposing this electrostatically charged surface to a light and shadow image. The light struck areas of the imaging layer are thus rendered conductive and the electrostatic charge selectively dissipated in these irradiated areas. After the photoconductor is exposed, the latent electrostatic image on this image bearing layer is rendered visible by development with a finely divided colored electroscopic material, known in the art as "toner". This toner will be principally attracted to those areas on the surface of the imaging layer which retain the electrostatic charge and thus render visible the latent image.
The developed image can then be read or permanently affixed to the photoconductor where the imaging surface is not to be reused. This latter practice is usually followed with respect to the binder type photoconductive films (e.g. zinc oxide pigment dispersed in a film forming insulating resin) where the photoconductive imaging layer is also an integral part of the finished copy.
In so-called "plain paper" copying systems, the latent image can be developed on a reusable photoconductive layer or transferred to another surface, such as a sheet of paper, and thereafter developed. When the latent image is developed on the imaging surface of a reusable photoconductive layer, it is subsequently transferred to another substrate and then permanently affixed thereto. Any one of a variety of well known techniques can be used to permanently affix the toner image to the copy sheet, including overcoating with transparent films, and solvent or thermal fusion of the toner particles to the supportive substrate.
In the above "plain paper" copying systems, the materials used in the photoconductive layer should preferably be capable of rapid switching from insulative to conductive to insulative state in order to permit cyclic use of the imaging layer. The failure of the material to return to its relatively insulative state prior to succeeding charging sequence will result in a decrease in the maximum charge acceptance of the photoreceptor. This phenomenon, commonly referred to in the art as "fatigue", has in the past been avoided by the selection of photoconductive materials possessing rapid switching capacity. Typical of the materials suitable for use in such a rapidly cycling imaging system include anthracene, sulfur, selenium and mixtures thereof (U.S. Pat. No. 2,297,691); selenium being preferred because of its superior photosensitivity. In order to further enhance the spectral range and/or electrophotographic response of selenium, selenium has been alloyed with materials such as tellurium and arsenic, U.S. Pat. Nos. 2,745,327 (Te/Se); and 2,803,542 (As/Se); 2,822,300 (As/Se); 3,312,548 (As/Sd & halogen).
Although selenium and selenium alloys probably are the most desirable materials from which to fashion the imaging layer of a photoconductive imaging member, imaging layers of these materials do have some serious physical limitations. For example, imaging layers of amorphous selenium and selenium alloys are sensitive to abrasion. Moreover, the adhesion of vaccuum deposited selenium on many of the conductive substrates used in electrophotography is relatively poor. Poor adhesion of imaging layers prepared from such materials does not, however, cause impairment of the integrity of the imaging member so long as the conductive substrate bearing this imaging layer is inflexible. Recently, there has been increasing interest in the use of flexible photoconductors due to the greater freedom in machine design and increased speed in copier throughput permitted by the use of such flexible imaging members. Unfortunately, because of the brittle nature of amorphous selenium and selenium alloy imaging layers, coupled with relatively poor adhesion to most conventional conductive substrates, such materials do not readily lend themselves to fabrication of flexible imaging members since repeated flexure of the member can result in cracking and separation of the imaging layer from the conductive substrate.
One technique suggested for the resolution of this problem is the provision of an interfacial layer intermediate between the conductive substrate and an imaging layer of amorphous selenium or selenium alloy, U.S. Pat. Nos. 3,713,821 and 3,671,467 (of which the instant application is a continuation-in-part). These interfacial layers reportedly provide improved adhesion between the imaging layer and the conductive substrate. The interlayer disclosed in '467 comprises a polymeric seleno-organic material having recurring units of the formula EQU Se -- A -- Se I
wherein
A is a member selected from the group consisting of an alkylene radical having from 9 to 50 carbon atoms, a divalent aromatic or a substituted aromatic radical having from 6 to 50 carbon atoms and heterocyclic radicals. PA1 B is a member selected from the group consisting of a divalent hydrocarbylene radical and a divalent heretocyclic radical; PA1 a is a positive integer of at least 3; and PA1 b is a positive integer greater than 1. PA1 A is a member selected from the group consisting of an alkylene radical having from about 9 to about 20 carbon atoms, a divalent aromatic radical having from about 6 to about 50 carbon atoms and a divalent heterocyclic radical; PA1 m is at least 1; and PA1 n is at least 2. PA1 B is a member from the group consisting of a divalent hydrocarbylene radical and a divalent heterocyclic radical PA1 a is a positive integer of at least 2; PA1 x is a positive integer of at least 1 but less than a; PA1 m is a positive integer in excess of 1; and PA1 b is a positive integer in excess of 1.
or EQU B -- Se.sub.a b II
wherein
Although many of the polymers having recurring units of formula I and all of the polymers having recurring units of formula II are reportedly intrinsically photoconductive, the spectral response and electrophotographic speed of such materials is somewhat limited.
Accordingly, it is the object of this invention to provide a polymeric photoconductive composition free from the limitations possessed by the above materials.
More specifically, it is the object of this invention to provide a polymeric photoconductive material having enhanced abrasion resistance.
Another object of this invention is to provide a polymeric photoconductive composition suitable in preparation of flexible photoconductive imaging members by virtue of its enhanced adhesion to flexible conductive substrates.
Yet another object of this invention is to provide a polymeric photoconductive composition having enhanced spectral response and a more rapid rate of light discharge.
Still yet another object of this invention is to provide a method for controlling the photoresponse of organo-selenium polymers and a method for controlling the photoresponse of tellurium.
A further object of this invention is to provide a polymeric photoconductive composition which readily lends itself to a continuous process for the manufacture of electrophotographic imaging members.
Still further objects of this invention include providing flexible electrophotographic imaging members prepared from the above photoconductive compositions and imaging processes using such flexible imaging members.